Method for feeding dry coal to superatmospheric pressure

ABSTRACT

A method for continuous feeding of dry coal particles from essentially atmospheric pressure to the superatmospheric pressure level of a coal gasifier or coal liquefaction reactor is achieved by a series of screw feeding devices each partially boosting the pressure level of the coal in stages to provide the dry coal at reactor pressure.

United States Patent [191 Hoffert et al.

[ Nov. 27, 1973 METHOD FOR FEEDING DRY COAL TO SUPERATMOSPHERICPRESSURE,

Inventors: Franklin D. Hoffert, Mountainside;

Harold H. Stotler, Westfield, both of N .J

Assignee: Hydrocarbon Research, Inc., New

1 York, NY.

Filed: July 20, 1971 Appl. No.: 164,381

US. Cl. 48/197 R, 48/63, 48/73, 48/202, 48/206, 208/8, 214/17 B,252/373,

Int. Cl. C10g 1/06, C10j 3/16, C10j 3/50 Field of Search 48/63, 64, 73,76, 48/77, 78, 99, 101, 197 R, 202, 203, 204,

Cool 10 Aimospherlc 0001 Ho er E PP Inert Gus Pur e Gas Recycle 68 Comressor 42 Recycle Gus (Hydrogen) '[56] References Cited UNITED STATESPATENTS 2,831,587 4/1958 Rearick 214/17 8 3,519,555 7/1970 Keith et a1.208/10 3,226,204 12/1965 Stotler et a1. 48/202 X 3,175,890 3/1965 Textor48/203 X Primary Examiner-Joseph Scovronek Attorney-Nathaniel Ely et a1.

[57] ABSTRACT A method for continuous feeding of dry coal particles fromessentially atmospheric pressure to the superatmospheric pressure levelof a coal gasifier or coal 1i quefaction reactor is achieved by a seriesof screw feeding devices each partially boosting the pressure level ofthe coal in stages to provide the dry coal at reactor pressure.

2 Claims, 1 Drawing Figure Reactor PATENTEDuuv 2? 1913 3775071 Cool I02Atmospheric Cool Hopper Inert Gos G05 Surge 22 I6 Pur e 605 Drum 45Scrubber 24 78 66 l 2 W @y L 64 I A CowlPFrlessure iii-F oe opper C H2OVent Gas 26 7O Recycle rL f r Reoclor i2 60B 74 Compressor Cg ControllerL H.P.C.H.

Level I 48 Controller 46 r M f 42 36 Flow Recycle Gas 7 Controller(Hydrogen) I l METHOD FOR FEEDING DRY COAL TO SUPERATMOSPHERIC PRESSUREBACKGROUND OF THE INVENTION In the gasification of coal to producesynthesis gas for the manufacture of hydrogen or ammonia and to producepipeline gas, the coal is gasified at pressures ranging from 400 to 1200psig. In the hydrogenation of coal to produce liquid hydrocarbons thecoal is liquefied at pressures ranging from 500 to 3000 psig. The coal,usually as pulverized particles, can be charged to thesesuperatmospheric pressure systems as dry particles by the conventionallock hopper system. Here the coal is fed to a lock hopper at essentiallyatmospheric pressure. The lock hopper is then pressurized with a highpressure gas stream from the coal conversion system. The coal which isnow under a pressure higher than the gasifier or hydrogenation systempressure is then transferred through piping to the coal conversionsystem. The lock hopper now empty of coal but filled with pressurizedgas is then depressured to essentially atmospheric pressure and the coalcharging cycle is repeated.

This method for feeding the dry coal has the disadvantage of a high lossof pressured gas during the depressuring'part of the charging cycle andlarge lock hopper volumes are required for commercial coal gasificationand liquefaction plants due to intermittent feeding from the lockhoppers.

Another method for feeding pulverized coal to a pressurized system is bymixing the pulverized coal with a liquid such as water or oil to producea slurry which can then be pumped into the superatmospheric pressuresystem. This method has the disadvantage of low throughput for a givenslurry pump and an expensive slurry pump design to provide a pump inwhich erosion is minimized. It also suffers the disadvantage that theliquid used to prepare the slurry must be recovered, usually byvaporization and recondensation, in the system so that it can berecycled back to be used to charge additional coal to the system.

In this invention a method is provided for feeding dry pulverized coalcontinuously to a system operating at superatmospheric pressure wherebythe lock hopper volume, and the loss of pressurized gas are minimizedand since the coal is fed dry no recovery of slurrying liquid isrequired.

SUMMARY OF THE INVENTION DESCRIPTION OF THE DRAWING The drawing is aschematic flow diagram of equipment for feeding coal to a coalconversion reactor.

DESCRIPTION OF PREFERRED EMBODIMENT A coal such as bituminous,semibituminous. subbituminous or lignite or a similar material such asshale, is initially elevated to the inlet 10 of the atmospheric coalhopper 12 as by elevator. not shown. Preferably, such coal haspreviously been surface dried and ground to a desired mesh ashereinafter described.

The coal fines discharging into the atmospheric coal hopper 12 may bepurged of air if desired with inert gas at 14 and with purge gas fromthe coal liquefaction system at 16.

The coal then enters the screw feeder 20 which is appropriately drivenby motor 22 and by which the coal can be boosted to 215 psig anddischarged into the low pressure coal hopper 24. Ultimately, the coalthen discharges into the next suitable screw feeder 26, therebyincreasing the pressure to 430 psig.

In turn, the coal discharges into the intermediate pressure coal hopper(lPCI-i) 28 and in due course drops into the third screw feeder 30.Thereby the pressure on the coal is thus raised to the pressure in thehigh pressure hopper (HPCH) 32 of approximately 645 psig. From this highpressure coal hopper 32, the coal then discharges into the screw feeder36 again to be boosted in pressure and discharging into the transferline 40 at approximately 750-850 psig.

The transfer line 40 is fed with recycle gas from the coal liquefactionsystem at 42 which transports the coal in a dense phase condition intothe coal reactor 45.

As described in US. Patents Nos., RE.25,770 and 3,519,555, which relateto coal liquefaction, the environment within the reactor 45 is liquidphase as a result of the feed of hydrogen at 46 at such temperature andpressure as will convert the coal to liquid condition. Some supplementalliquid maybe introduced at 48 if desired. The reactor 45 can contain anebullated bed of catalyst to promote the rate of conversion.

The conditions in reactor 45 being such as to continuously convert thesolid coal to liquid and gas, the gas is removed at 50 and the liquidand unconverted coal are removed through the down pipe 52.

The type of screw feeder shown in the drawing at 20, 26, 30 and 36 is ahigh speed screw pump which can pump the solids against a pressuredifferential in the order of 215 pounds per square inch. Hence, if thereaction chamber is at 750 psig, four stages are adequate whereas if ahigher pressure is desirable, additional screw pumps can be used. Suchpumps are commercially available from Fuller Co. (Fuller-Kenyon pump)and from Robbins & Meyers (Moyno pump).

A particular advantage of the screw pump is that there is a continuousuniform increase in pressure with no substantial gas loss or solidsbackflow. The operation is continuous which is particularly beneficialin the hydrogenation of coal or the gasification of coal.

To maintain appropriate pressures in the respective coal hoppers, wehave shown a gas circulating system wherein the gas from coal hoppers24, 28 and 32 pass through back pressure control valves 60 A, 60 B and60 C respectively and into line 62 to scrubber 64 where it isappropriately scrubbed with water. The gas then enters surge drum 66from which it can .be recompressed by compresser 68 into the line 70.

Under control of valve 72, appropriately pressurized gas will passthrough line 74 into the intermediate pressure coal hopper 28 and undercontrol of the valve 16 and line 78 into the low pressure coal hopper24. By line 80, it will pass into the high pressure coal hopper 32. Thesolids levels in coal hoppers 24, 28 and 32 are controlled by the speedof the screw feeding device. The speed of screw feeder 36 is controlledby the flow of gas and solids to reactor 45 in line 90 as by a flowcontroller.

As a result of such operation, there is a minimum loss of recycle gaswhich may, of course, be recovered by suitable means from the gasoverhead line 50.

A comparison of the dry feed with a slurry feed for a 100,000 BPSDrefinery indicates a saving of capital investment of nearly 70% ($7.2 MMvs. $2.3 MM).

The operation cost for charging the coal shows an annual savings ofnearly 70 percent ($2.8 MM vs. $0.9 MM) which, based on gasoline cost,would show a saving of about 0.14 cents/gallon gasoline.

Preferred operating conditions in the coal liquefaction reactor would bein a pressure range of 500 to 3000 psi hydrogen partial pressure, atemperature range in the order of 750900F, a typical hydrogenationcatalyst such as cobalt molybdate on alumina, the coal being predried toa moisture content not to exceed five weight percent, and with a coalsize of less than one-fourth inch.

Preferred operating conditions for a coal gasifier, such as disclosed inUS. Pat. No. 2,634,198 and No. 3,226,204, are as follows:

Temperature; 1 l-l 800F;

Pressure; atmosphere -l 450 psig, usually above 450 psig.

While we have shown and described a preferred form of embodiment of ourinvention, we are aware that modifications may be made within the scopeand spirit thereof.

We claim:

1. In a method of hydroconversion of coal wherein the coal inparticulate form and hydrogen are passed upwardly through a reactionzone in a liquid phase environment under hydrogenation conditions oftemperature in the range of 750900F and hydrogen partial pressures inthe range of 500 psi to 3000 psi with the removal of liquid and gaseouseffluent from the reaction zone, the improvement which comprises:

a. drying and grinding the coal to a moisture content of not to exceedfive weight percent and a grind less than V4 inch;

b. mechanically boosting the pressure on said coal solids in stages fromatmospheric to reaction zone pressure by use of high speed screw pumps;

c. introducing said pressurized, substantially dry coal particles intothe reaction zone independent of a carrier liquid; and

d. simultaneously measuring and controlling the weight flow of coalparticles into the reaction zone to provide a constant weight flow ofcoal into the reaction zone.

2. In a method of gasification of coal wherein the coal in particulateform and reactant gases are passed upwardly through a reaction zoneunder conversion conditions of temperatures up to 1800F and pressure upto 1450 psig for the gasification of the coal, the improvement whichcomprises:

a. drying and grinding the coal to a moisture content of not to exceedfive weight percent and a grind less than V4 inch;

b. mechanically boosting the pressure on said coal solids in stages fromatmospheric to reaction zone pressure by use of high speed screw pumps;

c. introducing said pressurized, substantially dry coal particles intothe reaction zone in the absence of a carrier liquid; and

(1. simultaneously measuring and controlling the weight flow of coalparticles into the reaction zone to provide a constant weight flow ofcoal into the reaction zone.

t i l

2. In a method of gasification of coal wherein the coal in particulateform and reactant gases are passed upwardly through a reaction zoneunder conversion conditions of temperatures up to 1800*F and pressure upto 1450 psig for the gasification of the coal, the improvement whichcomprises: a. drying and grinding the coal to a moisture content of notto exceed five weight percent and a grind less than 1/4 inch; b.mechanically boosting the pressure on said coal solids in stages fromatmospheric to reaction zone pressure by use of high speed screw pumps;c. introducing said pressurized, substantially dry coal particles intothe reaction zone in the absence of a carrier liquid; and d.simultaneously measuring and controlling the weight flow of coalparticles into the reaction zone to provide a constant weight flow ofcoal into the reaction zone.